Flagrum, you seem to have an issue (and that's fine, I'm not insulting you) with the exhaust molecules rebounding or not off the chute. Let's say they stay very close to the chute: after a while, you'll have a region of high pressure, and a pressure gradient. Then, even if the chute is "sticky" like you think, you will have to have a flow of fluid out of the chute.
I don't know very much about materials science (a few courses in solid state physics, but I'm a high-energy theorist), but I'm sure the gas molecules will not stick just because the chute is fabric/soft/bendy/whatever. That's a special scenario, which requires special circumstances. The general case is that the gas molecule will rebound in some direction with some fraction of its kinetic energy. I see no reason why that should be 0, and the fan-into-sail experiment (done by laymen, sure) seems to support that.
Also, more on topic, I have no idea if this is modelled in DCS or if this behaviour actually is unintended (I suspect the latter since turbulence isn't modelled); all I'm saying is that it isn't as unphysical as the first few posters in this thread thought.